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1
Lopresti, Mattia. "Non-destructive X-ray based characterization of materials assisted by multivariate methods of data analysis: from theory to application." Doctoral thesis, Università del Piemonte Orientale, 2022. http://hdl.handle.net/11579/143020.
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X-ray based non-destructive techniques are an increasingly important tool in many fields, ranging from industry to fine arts, from medicine to basic research. Over the last century, the study of the physical phenomena underlying the interaction between X-rays and matter has led to the development of many different techniques suitable for morphological, textural, elementary, and compositional analysis. Furthermore, with the development of the hardware technology and its automation thanks to IT advancements, enormous progress has been made also from the point of view of data collection and nowadays it is possible to carry out measurement campaigns by collecting many GigaBytes of data in a few hours. Already huge data sets are further enlarged when samples are analyzed with a multi-technique approach and/or at in situ conditions with time, space, temperature, and concentration becoming additional variables. In the present work, new data collection and analysis methods are presented along with applicative studies in which innovative materials have been developed and characterized. These materials are currently of high application interest and involve composites for radiation protection, ultralight magnesium alloys and eutectic mixtures. The new approaches have been grown up from an instrumental viewpoint and with regard to the analysis of the data obtained, for which the use and development of multivariate methods was central. In this context, extensive use has been made of principal component analysis and experimental design methods. One prominent topic of the study involved the development of in situ analysis methods of evolving samples as a response to different types of gradients. In fact, while in large structures such as synchrotrons carrying out analyzes under variable conditions is now consolidated practice, on a laboratory scale this type of experiments is still relatively young and the methods of data analysis of data sets evolving systems have large perspectives for development especially, if integrated by multivariate methods.
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Shinozaki, Osamu, Hirohide Furutani, Masaki Misawa, Naoki Takada, Kazuki Yamauchi, and Kazuhiro Yamamoto. "Lattice Boltzmann simulation on continuously regenerating diesel filter." The Royal Society, 2011. http://hdl.handle.net/2237/20056.
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Lonie, Sandra. "A molecular dynamics simulation study of diffuse x-ray scattering from Câ†1â†0Hâ†1â†6." Thesis, University of Aberdeen, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.287696.
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Adamantane C10H16 is an interesting archetypal plastic crystal which has been extensively studied. It undergoes transition from a low temperature ordered phase to a high temperature disordered phase at T=208.6K. The C10H16 molecule has tetrahedral symmetry and the orientational disorder to the plastic phase has been interpreted in terms of the distribution of the molecules between two equally preferred orientations. A molecular dynamics simulation of C10H16 has been carried out using the CCP5 Library program moliq-dynamo, written by Dr. D Fincham of Keele University. The simulation model consists of rigid molecules interacting with an atom-atom pairwise additive potential. The dynamics of the adamantane molecules in the plastic phase have been investigated and results have been compared with previous work. The molecular trajectories generated by the simulation have been used to evaluate the intensity of diffuse x-ray scattering from the crystal. Results have been compared with experimental data obtained from energy-dispersive x-ray scattering measurements made at the Daresbury SRS. Using a series of simplified models of the crystal, the relative contributions to the scattered intensity from translational and orientational disorder have been investigated.
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Liu, Yu. "Simulation study on PEM fuel cell gas diffusion layers using X-ray tomography based Lattice Boltzmann method." Thesis, Loughborough University, 2011. https://dspace.lboro.ac.uk/2134/9254.
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The Polymer Electrolyte Membrane (PEM) fuel cell has a great potential in leading the future energy generation due to its advantages of zero emissions, higher power density and efficiency. For a PEM fuel cell, the Membrane-Electrode Assembly (MEA) is the key component which consists of a membrane, two catalyst layers and two gas diffusion layers (GDL). The success of optimum PEM fuel cell power output relies on the mass transport to the electrode especially on the cathode side. The carbon based GDL is one of the most important components in the fuel cell since it has one of the basic roles of providing path ways for reactant gases transport to the catalyst layer as well as excess water removal. A detailed understanding and visualization of the GDL from micro-scale level is limited by traditional numerical tool such as CFD and experimental methods due to the complex geometry of the porous GDL structural. In order to take the actual geometry information of the porous GDL into consideration, the x-ray tomography technique is employed which is able to reconstructed the actual structure of the carbon paper or carbon cloth GDLs to three-dimensional digital binary image which can be read directly by the LB model to carry out the simulation. This research work contributes to develop the combined methodology of x-ray tomography based the three-dimensional single phase Lattice Boltzmann (LB) simulation. This newly developed methodology demonstrates its capacity of simulating the flow characteristics and transport phenomena in the porous media by dealing with collision of the particles at pore-scale. The results reveal the heterogeneous nature of the GDL structures which influence the transportation of the reactants in terms of physical parameters of the GDLs such as porosity, permeability and tortuosity. The compression effects on the carbon cloth GDLs have been investigated. The results show that the c applied compression pressure on the GDLs will have negative effects on average pore size, porosity as well as through-plane permeability. A compression pressure range is suggested by the results which gives optimum in-plane permeability to through-plane permeability. The compression effects on one-dimensional water and oxygen partial pressures in the main flow direction have been studied at low, medium and high current densities. It s been observed that the water and oxygen pressure drop across the GDL increase with increasing the compression pressure. Key Words: PEM fuel cell, GDL, LB simulation, SPSC, SPMC, x-ray tomography, carbon paper, carbon cloth, porosity, permeability, degree of anisotropy, tortuosity, flow transport.
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Yamamoto, Kazuhiro. "Boundary Conditions for Combustion Field and LB Simulation of Diesel Particulate Filter." Global Science Press, 2013. http://hdl.handle.net/2237/20029.
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Liu, Fang. "Monte Carlo modeling of an x-ray fluorescence detection system by the MCNP code." Thesis, Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/33959.
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An x-ray fluorescence detection system has been designed by our research group for quantifying the amount of gold nanoparticles presented within the phantom and animals during gold nanoparticle-aided cancer detection and therapy procedures. The primary components of the system consist of a microfocus x-ray source, a Pb beam collimator, and a CdTe photodiode detector. In order to optimize and facilitate future experimental tasks, a Monte Carlo model of the detection system has been created by using the MCNP5 code. Specifically, the model included an x-ray source, a Pb collimator, a CdTe detector, and an acrylic plastic phantom with four cylindrical columns where various materials such as gold nanoparticles, aluminum, etc. can be inserted during the experiments. In this model, 110 kVp x-rays emitted into a 60o cone from the focal spot of the x-ray source were collimated to a circular beam with a diameter of 5 mm. The collimated beam was then delivered to the plastic phantom with and without a gold nanoparticle-containing column. The fluence of scattered and gold fluorescence x-rays from the phantom was scored within the detector's sensitive volume resulting in various photon spectra and compared with the spectra acquired experimentally under the same geometry. The results show that the current Monte Carlo model can produce the results comparable to those from actual experiments and therefore it would serve as a useful tool to optimize and troubleshoot experimental tasks necessary for the development of gold nanoparticle-aided cancer detection and therapy procedures.
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Stångberg, Valgeborg Fredrik. "Toward a Novel Gas Cell for X-Ray Spectroscopy : Finite Element Flow Simulation and Raman Characterization." Thesis, Uppsala universitet, Molekyl- och kondenserade materiens fysik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-394134.
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The new millennium has seen revolutionary advances in photonsource technology. As the newly constructed synchrotron facilityMAX IV in Lund, Sweden, pushes brilliance toward what isphysically possible, low-yield spectroscopic techniques, such asresonant inelastic X-ray scattering (RIXS), open new doors inmolecular and condensed matter research. The VERITAS beamline atMAX IV is designed for high-resolution vibrational RIXS on gases.X-rays interact with flowing molecules inside a window-cappedcell, but the radiation intensity is expected to be large enoughto damage the windows, and cause build-up of photochemicalproducts, which lowers transmission. To address these issues, anovel gas cell design is presented, wherein the distance betweensample gas and window is increased by using a flowing heliumbuffer. The main challenge is maintaining a steep sample gasconcentration gradient within the cell, and to that end, gas flowswere simulated on various geometries by using the finite elementmethod to solve the Navier-Stokes equations. Results were used toconstruct a prototype, and confocal Raman microscopy was used forconcentration characterization. Preliminary measurements revealeda uniform sample gas distribution, and the technique proved to beinefficient for wide scanning of parameter values. This suggeststhat a supplementary experiment is required to find roughestimates of good parameter values, which can then be followed upwith new Raman measurements for fine-tuning of the properparameter space. Real-time visualization of the sample gas flow,using a visible gas under an optical microscope, is one candidatefor this supplementary experiment.
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Lester, Sonia. "A study of scattered radiation in diagnostic radiology using Monte Carlo simulation." Thesis, Institute of Cancer Research (University Of London), 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.287993.
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Henkel, Thilo Johannes. "Strain-related phenomena in (In,Ga)N/GaN nanowires and rods investigated by nanofocus x-ray diffraction and the finite element method." Doctoral thesis, Humboldt-Universität zu Berlin, 2018. http://dx.doi.org/10.18452/18707.
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In dieser Arbeit wird das lokal
aufgelöste Deformationsfeld einzelner (In,Ga)N/GaN Drähte mit Hilfe nanofokussierter
Röntgenbeugung und der Methode der Finiten Elemente untersucht. Hiermit
soll ein Beitrag zum grundlegenden Verständis der optischen Eigenschaften
geleistet werden, die durch das Deformationsfeld maßgeblich beeinflusst werden.
Zunächst wird die Abhängigkeit der vertikalen Normalkomponente, epsilon_zz, des
elastischen Dehnungstensors von der Geometrie eines axialen (In,Ga)N/GaN
Nanodrahtes diskutiert. Dabei wird ein signifikant negativer epsilon_zz-Wert beobachtet,
sobald das Verhältnis von Nanodrahtradius und (In,Ga)N-Segmentlänge gegen
eins strebt. Auffallend große Scherkomponenten und eine konvexe
Verformung der äußeren Oberfläche begleiten das Auftreten des negativen epsilon_zz-
Wertes und sind die Ursache dieses Effekts. Durch eine Ummantelung von GaN-Nanodrähten mit einer (In,Ga)N-Schale
lässt sich die aktive Fläche und somit die potentielle Lichtausbeute pro Fläche
im Vergleich zu planaren Strukturen deutlich erhöhen. Es wurde jedoch festgestellt,
dass das entlang der Drahthöhe emittierte Licht rotverschoben ist. Um
den Ursprung dieses Phänomens zu beleuchten, wird das lokale Deformationsfeld
mit Hilfe nanofokussierter Röntgenbeugung vermessen. Durch die gute
räumliche Auflösung ist es möglich, das Deformationsfeld innerhalb einzelner
Seitenfacetten zu untersuchen, wobei ein deutlicher Gradient festgestellt wird.
Basierend auf dem mit der Methode der Finiten Elemente simulierten Deformationsfeld
und kinematischen Streusimulationen, ist es möglich, den Deformationszustand
in einen In-Gehalt zu übersetzen. Wenn neben dem Deformationsfeld
auch der strukturelle Aufbau in der Simulation berücksichtigt wird, kann der
In-Gehalt mit noch größerer Genauigkeit bestimmt werden.In this thesis, nanofocus x-ray diffraction and the finite element method are applied to analyze the local strain field in (In,Ga)N/GaN nanowires and micro-rods which are discussed as candidates for a plethora of future optoelectronic applications. However, to improve and tailor their properties, a fundamental understanding on the level of individual objects is essential. In this spirit, the dependence of the vertical normal component, epsilon_zz, of the elastic strain tensor on the geometry of an axial (In,Ga)N/GaN nanowire is systematically analyzed using the finite element method. Hereby, it is found that if the ratio of nanowire radius and (In,Ga)N segment length approaches unity, a significantly negative epsilon_zz value is observed. This stands in stark contrast to naive expectations and shows that the common knowledge about planar systems where epsilon_zz would always be greater or equal zero cannot easily be translated to nanowires with an equivalent material sequence. As the origin of this effect significant shear strains are discussed which go along with a convex deformation of the outer surface resulting in a highly complex strain distribution. The increased active area of core-shell (In,Ga)N/GaN micro-rods makes them promising candidates for next-generation light emitting diodes. However, it is found that the emission wavelength is significantly red-shifted along the rod height. To shed light on the origin of this phenomenon, nanofocus x-ray diffraction is applied to analyze the local strain field. Due to the high spatial resolution it is possible to investigate the strain field within individual side-facets and to detect a significant gradient along the rod height. Based on the deformation field simulated using the finite element method and subsequent kinematic scattering simulations it is possible to translate the strain state into an In content.
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Philippov, Sergey. "Modelagem computacional para a interpretação de dados de medição de tensões mecânicas pelo método de difração de raios X." Universidade do Estado do Rio de Janeiro, 2006. http://www.bdtd.uerj.br/tde_busca/arquivo.php?codArquivo=326.
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Coordenação de Aperfeiçoamento de Pessoal de Nível SuperiorTensões mecânicas residuais próximas à superfície são importantes em relação às propriedades de materiais, como resistência, durabilidade, resistência a fricção etc. Muitos métodos modernos de tratamento de superfície produzem gradientes das tensões. Porém, até agora ainda não há um método de medição dos parâmetros destes gradientes, apesar de várias tentativas. A aplicação do método de difração de raios X ao problema é interessante pela possibilidade de avaliar os gradientes em camadas muito finas (~10m). Neste trabalho novos métodos como modelagem computacional, análise de Fourier e operação de convolução são aplicados à dados simulados que se obtêm pelo método de tensometria por raios X chamado método-sen2ψ. É mostrado que os gradientes de tensão produzem não-linearidades nas dependências experimentais e para gradientes fortes o suficiente estas não-linearidades podem ser registradas em experimento. São analisadas funções diferentes de distribuição de tensões e os efeitos que estas produzem para estados diferentes de tensões (uni-, bi- e tridimensional). É mostrado que a influência do gradiente pode ser descrita através da operação de convolução, e a função de gradiente pode ser obtida utilizando a transformada de Fourier e a operação de deconvolução. São estimados o menor valor de gradiente que pode ser registrado e a menor profundidade da distribuição não-homogênea de tensão que ainda tem efeito nos dados.
Residual stresses near the material surface are important for material's properties, like resistance, durability and friction resistance. A lot of modern methods of surface treatment produce stress gradients. However, up to now there is not a universal method of stress gradients parameters measurement, although various attempts were made. Aplication of X-ray diffraction method to the problem seems to be the best way to resolve it because of its possibility to measure the gradients in very thin layers (about 10m). Some new methods like computer simulation, Fourier analysis and operation of convolution are applied in this paper to simulate experimental data of X-ray tensometry method, called sin2ψ-method. It is shown that stress gradients produce non-linearities in the experimental dependences and for the gradients strong enough these non-linearities can be registered in experiment. There are analyzed different functions of stress distribution and the effects they produce for different stress states (one-, two- and three-dimensional). There is shown that the influence of gradient can be desribed by means of operation of convolution, and the gradient function can be found using Fourier transformation and deconvolution operation. It was estimated the smallest value of gradient that can be registered and the smallest depth of non-homogenious stress distribution that still has an effect on the data.
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Ma, Jiajie. "Accuracy and reliability of non-linear finite element analysis for surgical simulation." University of Western Australia. School of Mechanical Engineering, 2006. http://theses.library.uwa.edu.au/adt-WU2010.0089.
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In this dissertation, the accuracy and reliability of non-linear finite element computations in application to surgical simulation is evaluated. The evaluation is performed through comparison between the experiment and finite element analysis of indentation of soft tissue phantom and human brain phantom. The evaluation is done in terms of the forces acting on the cylindrical Aluminium indenter and deformation of the phantoms due to these forces. The deformation of the phantoms is measured by tracking 3D motions of X-ray opaque markers implanted in the direct neighbourhood under the indenter using a custom-made biplane X-ray image intensifiers (XRII) system. The phantoms are made of Sylgard® 527 gel to simulate the hyperelastic constitutive behaviour of the brain tissue. The phantoms are prepared layer by layer to facilitate the implantation of the X-ray opaque markers. The modelling of soft tissue phantom indentation and human brain phantom indentation is performed using the ABAQUSTM/Standard finite element solver. Realistic geometry model of the human brain phantom obtained from Magnetic Resonance images is used. Specific constitutive properties of the phantom layers determined through uniaxial compression tests are used in the model. The models accurately predict the indentation force-displacement relations and marker displacements in both soft tissue phantom indentation and human brain phantom indentation. Good agreement between the experimental and modelling results verifies the reliability and accuracy of the finite element analysis techniques used in this study and confirms the predictive power of these techniques in application to surgical simulation.
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Lübbert, Daniel. "Strain and lattice distortion in semiconductor structures : a synchrotron radiation study." Phd thesis, Universität Potsdam, 1999. http://opus.kobv.de/ubp/volltexte/2005/2/.
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Die Arbeit stellt neu entwickelte Röntgenbeugungsmethoden vor, mit deren Hilfe der Verzerrungszustand des Kristallgitters von Halbleiter-Wafern und -Bauteilen im Detail charakterisiert werden kann. Hierzu werden die aussergewöhnlichen Eigenschaften der an modernen Synchrotrons wie der ESRF (Grenoble) verfügbaren Röntgenstrahlung genutzt. Im ersten Teil der Arbeit werden Röntgen-Diffraktometrie und -Topographie zu einer Untersuchungsmethode kombiniert, mit der die makroskopische Krümmung von Halbleiter-Wafern ebenso wie ihre mikroskopische Defektstruktur abgebildet werden kann. Der zweite Teil ist der Untersuchung von epitaktisch gewachsenen und geätzten Oberflächengittern mit Abmessungen im Submikrometer-Bereich gewidmet. Die unterschiedlichen Gitterkonstanten der beteiligten Halbleitermaterialien führen zu einem inhomogenen Verzerrungsfeld in der Probe, das sich im Röntgenbild durch eine charakteristische Verformung des Beugungsmusters in der Umgebung der Bragg-Reflexe äussert. Die Analyse der experimentell gemessenen Beugungsmuster geschieht mit Hilfe eines neu entwickelten Simulationsverfahrens, das Elastizitätstheorie und eine semi-kinematische Röntgenbeugungstheorie miteinander verbindet. Durch quantitativen Vergleich der Simulationsergebnisse mit den Messdaten kann auf den genauen Verlauf des Verzerrungsfeldes in den Proben zurückgeschlossen werden. Dieses Verfahren wird erfolgreich auf verschiedene Halbleiter-Probensysteme angewendet, und schliesslich auch auf die Untersuchung von akustischen Oberflächenwellen in Halbleiterkristallen übertragen.
This thesis presents newly developed X-ray methods which can be used to characterize in detail the state of distortion of the crystal lattice in semiconductor wafers, devices and nanostructures. The methods use the extraordinary properties of the X-rays available from modern synchrotron sources such as the ESRF (Grenoble).
In the first part of the thesis, X-ray diffractometry and X-ray topography are combined into a new method, called X-ray rocking curve imaging, which allows to image the macroscopic curvature of semiconductor wafers as well as the underlying microscopic defect structure. The second part of the thesis deals with the investigation of epitaxially grown and subsequently etched semiconductor gratings with lateral periods below the micrometer. The lattice mismatch between the different materials used in heteroepitaxy leads to a non-uniform strain field in the sample, which is reflected in a characteristic distortion of the X-ray diffraction pattern around each Bragg peak. The experimental data are evaluated with the help of a newly developed simulation procedure which combines elasticity theory with a semi-kinematical theory of X-ray diffraction. From a quantitative comparison of measured and simulated data the detailed shape of the strain field in the samples can be deduced. This procedure is used successfully for the structural characterization of different types of semiconductor gratings, and is finally applied also to the investigation of surface acoustic waves in crystals.
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Su, Ting. "Quantitative material decomposition methods for X-ray spectral CT." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSEI056/document.
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La tomographie (CT) aux rayons X joue un rôle important dans l'imagerie non invasive depuis son introduction. Au cours des dernières années, de nombreuses avancées technologiques en tomographie par rayons X ont été observées, notamment la CT spectrale, qui utilise un détecteur à comptage de photons (PCD) pour discriminer les photons transmis correspondant à des bandes d'énergie sélectionnées afin d'obtenir une information spectrale. La CT spectrale permet de surmonter de nombreuses limitations des techniques précédentes et ouvre de nombreuses applications nouvelles, parmi lesquelles la décomposition quantitative des matériaux est le sujet le plus étudié. Un certain nombre de méthodes de décomposition des matériaux ont été rapportées et différents systèmes expérimentaux sont en cours de développement pour la CT spectrale. Selon le type de données sur lequel l'étape de décomposition fonctionne, nous avons les méthodes du domaine des projections (décomposition avant reconstruction) et les méthodes du domaine de l'image reconstruite (décomposition après reconstruction). La décomposition couramment utilisée est basée sur le critère des moindres carrés, nommée proj-LS et méthode ima-LS. Cependant, le problème inverse de la décomposition du matériau est généralement mal posé et les mesures du CT spectral aux rayons X souffrent de bruits de comptage de photons de Poisson. Le critère des moindres carrés peut conduire à un surajustement des données de mesure bruitées. Dans le présent travail, nous avons proposé un critère de moindre log-carré pour la méthode du domaine de projection afin de minimiser les erreurs sur le coefficient d'atténuation linéaire: méthode proj-LLS. De plus, pour réduire l'effet du bruit et lisser les images, nous avons proposé d'ajouter un terme de régularisation par patch pour pénaliser la somme des variations au carré dans chaque zone pour les décompositions des deux domaines, nommées proj-PR-LLS et ima -PR-LS méthode. Les performances des différentes méthodes ont été évaluées par des études de simulation avec des fantômes spécifiques pour différentes applications: (1) Application médicale: identification de l'iode et du calcium. Les résultats de la décomposition des méthodes proposées montrent que le calcium et l'iode peuvent être bien séparés et quantifiés par rapport aux tissus mous. (2) Application industrielle: tri des plastiques avec ou sans retardateur de flamme. Les résultats montrent que 3 types de matériaux ABS avec différents retardateurs de flamme peuvent être séparés lorsque l'épaisseur de l'échantillon est favorable. Enfin, nous avons simulé l'imagerie par CT spectrale avec un fantôme de PMMA rempli de solutions de Fe, Ca et K. Différents paramètres d'acquisition, c'est-à-dire le facteur d'exposition et le nombre de bandes d'énergie, ont été simulés pour étudier leur influence sur la performance de décomposition pour la détermination du ferX-ray computed tomography (X-ray CT) plays an important part in non-invasive imaging since its introduction. During the past few years, numerous technological advances in X-ray CT have been observed, including spectral CT, which uses photon counting detectors (PCDs) to discriminate transmitted photons corresponding to selected energy bins in order to obtain spectral information with one single acquisition. Spectral CT enables us to overcome many limitations of the conventional CT techniques and opens up many new application possibilities, among which quantitative material decomposition is the hottest topic. A number of material decomposition methods have been reported and different experimental systems are under development for spectral CT. According to the type of data on which the decomposition step operates, we have projection domain method (decomposition before reconstruction) and image domain method (decomposition after reconstruction). The commonly used decomposition is based on least square criterion, named proj-LS and ima-LS method. However, the inverse problem of material decomposition is usually ill-posed and the X-ray spectral CT measurements suffer from Poisson photon counting noise. The standard LS criterion can lead to overfitting to the noisy measurement data. In the present work, we have proposed a least log-squares criterion for projection domain method to minimize the errors on linear attenuation coefficient: proj-LLS method. Furthermore, to reduce the effect of noise and enforce smoothness, we have proposed to add a patchwise regularization term to penalize the sum of the square variations within each patch for both projection domain and image domain decomposition, named proj-PR-LLS and ima-PR-LS method. The performances of the different methods were evaluated by spectral CT simulation studies with specific phantoms for different applications: (1) Medical application: iodine and calcium identification. The decomposition results of the proposed methods show that calcium and iodine can be well separated and quantified from soft tissues. (2) Industrial application: ABS-flame retardants (FR) plastic sorting. Results show that 3 kinds of ABS materials with different flame retardants can be separated when the sample thickness is favorable. Meanwhile, we simulated spectral CT imaging with a PMMA phantom filled with Fe, Ca and K solutions. Different acquisition parameters, i.e. exposure factor and number of energy bins were simulated to investigate their influence on the performance of the proposed methods for iron determination
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Renaud, Gilles. "Ordre chimique et désordre topologique dans les solutions solides AuNi : étude par résistivité et par absorption et diffusion du rayonnement synchrotron X." Grenoble 1, 1988. http://www.theses.fr/1988GRE10134.
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Caracterisation precise de la tendance a l'ordre a courte distance dans le monocristal au::(80) ni::(20): l'alliage est aleatoire en premier voisin, mais il existe une faible tendance a l'homocoordination en second voisin. Determination dans tout le domaine de composition des valeurs des trois distances moyennes partielles ainsi que de la largeur et de l'asymetrie de leur distribution. Mesure de l'effet de coeur dans les alliages dilues. Simulation par ordinateur des distorsions du reseau. Evaluation selon un modele harmonoque de l'energie elastique
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Golchert, Dennis J. "Application of X-ray microtomography to discrete element method simulations of agglomerate breakage /." St. Lucia, Qld, 2003. http://www.library.uq.edu.au/pdfserve.php?image=thesisabs/absthe17509.pdf.
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Silga, Matthias. "Elaboration de monocristaux de hgi::(2) alpha par la methode du flux force : application a la detection de rayonnements X gamma et alpha." Clermont-Ferrand 2, 1986. http://www.theses.fr/1986CLF21009.
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Elaboration de monocristaux hg1::(2)-alpha en vue de leur utilisation comme detecteurs de rayonnements. La purification du materiau de base, le controle du transport de matiere, le controle de la sursaturation a l'interieur des ampoules de croissance, la monogermination et l'etude de la morphologie du cristal sont traites en relation avec les proprietes de detection. Une approche theorique par simulation monte-carlo de la reponse d'un detecteur hgi::(2) a ete faite
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Wang, Yongping. "Digital Simulative Test of Asphalt Mixtures Using Finite Element Method and X-Ray Tomography Images." Diss., Virginia Tech, 2007. http://hdl.handle.net/10919/28748.
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Simulative tests, such as asphalt pavement analyzer (APA), Hamberg rut tester etc. have been widely used to evaluate the performance of asphalt mixtures. However, simulative tests to evaluate the performance of the mixtures cannot give fundamental properties of Asphalt Concrete (AC) due to the complex stress and strain fields. On the other hand, due to the availability of high-performance computing systems and software, numerical techniques are gaining popularity. This dissertation presents a computational simulation method of the APA tests in order to evaluate the rutting potential of asphalt mixtures based on actual microstructure reconstructed from X-ray tomography images. In the study, the microstructure of AC is obtained through the analysis of X-ray images, which included the digital information of the microstructure for the scanned specimen. In the simulations the three phases, mastic (asphalt binder with mineral filler), aggregates, and voids are assigned with different material properties. Aggregates are modeled as an elastic material, and air voids are removed during the loading steps. The adopted two-layer model is only used to represent the rate and temperature dependent behavior of the mastics.
The parameters are obtained with inverse methods. Based on the sensitivity analysis of the parameters, an iterative procedure is performed to optimize the parameters using the experimental measurement and results of the model simulations. A parametric study is also conducted to study the effect of major parameters such as the stiffness ratio of the networks on the macro response of the model. The simulation results obtained shows a good agreement with the experimental results.
The dissertation also presents a method to measure micro strains in asphalt mixture. An automated procedure using tomography images to reconstruct three-dimensional particles is developed. The translations of the particles are obtained from the coordinate differences of particles' mass centers before and after the APA testing. The micro and macro strains in the mixture are calculated based on the particle translations. A good correlation is found between measured strains and experimental result.Ph. D.
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Ning, Jing. "Computer simulation for medical imaging with x-rays using the Monte Carlo methods." Thesis, University of Ulster, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.232847.
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Cao, Weimin. "Theoretical and experimental studies of surface and interfacial phenomena involving steel surfaces." Doctoral thesis, KTH, Materialens processvetenskap, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-26194.
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The present work was initiated to investigate the surface- and interfacial phenomena for iron and slag/iron systems. The aim was to understand the mechanism of the effect of surface active elements on surface and interfacial properties. In the present work, the adsorption of oxygen and sulfur on iron surface as well as adatom surface movements were studied based on the ab initio method. BCC iron melting phenomena and sulfur diffusion in molten iron were investigated by Monte Carlo simulations. The impact of oxygen potential on interfacial mass transfer was carried out by X-ray sessile drop method. Firstly, the structural, electronic and magnetic properties as well as thermodynamic stability were studied by Density functional theory (DFT). The hollow site was found to be the most stable adsorption site both for oxygen and sulfur adsorbed on iron (100) surface, which is in agreement with the experiment. The relaxation geometries and difference charge density of the different adsorption systems were calculated to analyze the interaction and bonding properties between Fe and O/S. It can be found that the charge redistribution was related to the geometry relaxation. In addition, the sulfur coverage is considered from a quarter of one monolayer (1ML) to a full monolayer. It was found that the work function and its change Δφ increased with S coverage, in very good agreement with experiment. Due to a recent discussion regarding the influence of charge transfer on Δφ, it is shown in the present work that the increase in Δφ can be explained by the increasing surface dipole moment as a function of S coverage. S strongly interacts with the surface Fe layer and decreases the surface magnetic moment as the S coverage increases. Secondly, a two dimensional (2D) gas model based on density functional calculations combined with thermodynamics and statistical physics, was proposed to simulate the movement of the surface active elements, viz. oxygen and sulfur atoms on the Fe(100) surface. The average velocity of oxygen and sulfur atoms was found to be related to the vibration frequencies and energy barrier in the final expression developed. The calculated results were based on the density function and thermodynamics & statistical physics theories. In addition, this 2D gas model can be used to simulate and give an atomic view of the complex interfacial phenomena in the steelmaking refining process. A distance dependent atomistic Monte Carlo model was developed for studying the iron melting phenomenon as well as effect of sulfur on molten iron surface. The effect of boundary conditions on the melting process of an ensemble of bcc iron atoms has been investigated using a Lennard-Jones distance dependent pair potential. The stability of melting process was energetically and spatially analyzed under fixed wall and free surface conditions and the effects of short and long-range interactions were discussed. The role of boundary conditions was significantly reduced when long-range interactions were used in the simulation. This model was further developed for investigating the effect of sulfur on molten iron surface. A combination of fixed wall and free surface boundary condition was found to well-represent the molten bath configuration while considering the second nearest neighbor interactions. Calculations concerning the diffusion of sulfur on molten surface were carried out as a function of temperature and sulfur concentration. Our results show that sulfur atoms tended to diffuse away from the surface into the liquid bulk and the diffusion rate increased by increasing temperature. Finally, impact of oxygen potential on sulfur mass transfer at slag/metal interface, was carried out by X-ray sessile drop method. The movement of sulfur at the slag/metal interface was monitored in dynamic mode at temperature 1873 K under non-equilibrium conditions. The experiments were carried out with pure iron and CaO-SiO2-Al2O3-FeO slag (alumina saturated at the experimental temperature) contained in alumina crucibles with well-controlled partial pressures of oxygen and sulfur. As the partial pressure of oxygen increased, it was found that interfacial velocity as well as the oscillation amplitude increased. The thermo-physical and thermo-chemical properties of slag were also found to influence interfacial velocity.QC 20101123
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Moore, Zakhia. "Application of X-ray Diffraction Methods and Molecular Mechanics Simulations to Structure Determination and Cotton Fiber Analysis." ScholarWorks@UNO, 2008. http://scholarworks.uno.edu/td/888.
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The results of three very different studies are presented. X-ray diffraction has been utilized for single-crystal structure determinations, fiber diffraction analyses, and in conjunction with molecular modeling of Cellulose IIII. Although each technique is different in its sampling, data acquisition, data treatment, and identification, the common denominator has been the use of x-rays. The single-crystal structure determination of ethylene glycol bis(tropane-3-carboxylate) is presented as an example of the use of modern single-crystal x-ray instrumentation including the use of coupled charged devices (CCDs) as detectors for accurate data collection and rapid elucidation of crystal structures. The structure determination of Cellulose IIII by x-ray diffraction and computer modeling is presented to show how the use of x-rays in weakly diffracting materials can generate a reliable structure and be a key component in model building. Finally, a study is presented in which x-ray fiber diffraction data is utilized to investigate possible correlations between the crystallite orientation, crystallinity, crystallize size and the strength properties of cotton fibers collected from various countries.
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Jones, Cameron Christopher. "VALIDATION OF COMPUTATIONAL FLUID DYNAMIC SIMULATIONS OF MEMBRANE ARTIFICIAL LUNGS WITH X-RAY IMAGING." UKnowledge, 2012. http://uknowledge.uky.edu/cbme_etds/2.
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The functional performance of membrane oxygenators is directly related to the perfusion dynamics of blood flow through the fiber bundle. Non-uniform flow and design characteristics can limit gas exchange efficiency and influence susceptibility of thrombus development in the fiber membrane. Computational fluid dynamics (CFD) is a powerful tool for predicting properties of the flow field based on prescribed geometrical domains and boundary conditions. Validation of numerical results in membrane oxygenators has been predominantly based on experimental pressure measurements with little emphasis placed on confirmation of the velocity fields due to opacity of the fiber membrane and limitations of optical velocimetric methods.
A novel approach was developed using biplane X-ray digital subtraction angiography to visualize flow through a commercial membrane artificial lung at 1–4.5 L/min. Permeability based on the coefficients of the Ergun equation, α and β, were experimentally determined to be 180 and 2.4, respectively, and the equivalent spherical diameter was shown to be approximately equal to the outer fiber diameter. For all flow rates tested, biplane image projections revealed non-uniform radial perfusion through the annular fiber bundle, yet without flow bias due to the axisymmetric position of the outlet. At 1 L/min, approximately 78.2% of the outward velocity component was in the radial (horizontal) plane verses 92.0% at 4.5 L/min. The CFD studies were unable to predict the non-radial component of the outward perfusion.
Two-dimensional velocity fields were generated from the radiographs using a cross-correlation tracking algorithm and compared with analogous image planes from the CFD simulations. Velocities in the non-porous regions differed by an average of 11% versus the experimental values, but simulated velocities in the fiber bundle were on average 44% lower than experimental. A corrective factor reduced the average error differences in the porous medium to 6%. Finally, biplane image pairs were reconstructed to show 3-D transient perfusion through the device.
The methods developed from this research provide tools for more accurate assessments of fluid flow through membrane oxygenators. By identifying non-invasive techniques to allow direct analysis of numerical and experimental velocity fields, researchers can better evaluate device performance of new prototype designs.
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Kulkarni, Kanchan Avinash. "Experimental Characterization and Finite Element Simulation of Laser Shock Peening Induced Surface Residual Stresses using Nanoindentation." University of Cincinnati / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1352489043.
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Ohori, Shinya, and Kazuhiro Yamamoto. "Simulations on flow and soot deposition in diesel particulate filters." SAGE, 2013. http://hdl.handle.net/2237/20057.
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Sokoltsova, Tetiana. "Development of a standardless miniature XRF setup for the analysis of actinides : coupling MC methods with fundamental parameters." Thesis, université Paris-Saclay, 2021. http://www.theses.fr/2021UPASP018.
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La fluorescence des rayons X (XRF) est un outil analytique qualitatif et quantitatif pour la caractérisation élémentaire de nombreux types de matériaux ; elle est non destructive, rapide et convient à l'analyse d'une large gamme d'éléments. La méthode est basée sur l'excitation d'un analyte par un faisceau primaire de rayons X qui induit l'émission de la fluorescence X de l'échantillon. L'objectif de l'analyse quantitative par fluorescence X est d’établir la relation entre la concentration des éléments avec les intensités de fluorescence mesurées. Cependant, cette tâche n'est pas simple puisque les intensités de fluorescence apparentes dépendent de la fraction pondérale de l’élément dans l'analyte, de la composition de la matrice, de la géométrie du dispositif expérimental, des paramètres de la source de rayons X primaires et du système de détection, etc. Les informations quantitatives peuvent être obtenues en appliquant des approches théoriques ou empiriques. Un des objectifs de cette thèse est d'étudier les performances d’une installation miniaturisée de fluorescence X destinée à l'analyse des actinides par leurs raies XL (12 keV < E < 17 keV), implantée dans le laboratoire d’analyses de l’installation ATALANTE (CEA Marcoule). Le dispositif expérimental comprend un tube à rayons X à anode d'Ag qui irradie un échantillon, un détecteur au silicium à dérive (SDD) et un monochromateur HOPG cylindrique. Ce dernier élément est placé entre l'échantillon et le système de détection et agit comme un filtre passe-bande en modifiant la distribution spectrale du rayonnement de fluorescence. De cette manière, les spectres peuvent être enregistrés dans la gamme d'énergie d'intérêt, tout en réduisant le taux de comptage dû aux rayonnements parasites. Le monochromateur HOPG du dispositif expérimental couvre la gamme d'énergie d'intérêt qui permet d'analyser les éléments de Z moyen (Se, Rb, Sr, Y, etc.) et Z élevé (principalement U, Np, Pu, Am et Cm) par leurs raies K et L, respectivement. Le second objectif de ce travail est d'affiner l'algorithme classique de quantification basé sur les paramètres fondamentaux en tenant compte des modifications de la distribution spectrale par le cristal HOPG. En effet, les spectres mesurés avec un système de fluorescence classique peuvent être traités avec succès en utilisant une méthode théorique basée sur des équations mathématiques sans nécessiter d’étalons. Il s’agit de la méthode dite des paramètres fondamentaux (PF). Cependant, pour traiter avec précision les spectres mesurés avec la présente configuration, il est nécessaire de connaître la fonction de transmission du cristal HOPG. L'étude détaillée de l’instrumentation miniature et des phénomènes physiques mis en jeu a été réalisée en utilisant la méthode de Monte Carlo pour le transport des rayonnements, avec le code PENELOPE. Ensuite, pour mieux comprendre les propriétés de réflexion du cristal de HOPG, des simulations d’optique des rayons X ont été réalisées à l'aide du logiciel XRT afin de modéliser la réponse du cristal cylindrique de HOPG et représenter pas à pas l'ensemble de détection. La réponse du système optique développé a été simulée en utilisant des spectres expérimentaux enregistrés sans le monochromateur HOPG comme données d'entrée. Le modèle de simulation a été validé par la comparaison avec des données expérimentales pour différents échantillons liquides contenant des éléments Z moyens (quelques dizaines de mg.L-1), ce qui a permis de caractériser la fonction de transfert du cristal HOPG. Ensuite, celle-ci a pu être importée avec succès dans le logiciel PyMCA, basé sur les paramètres fondamentaux, afin de fournir des résultats quantitatifs. Pour conclure, il est démontré que le couplage du code Monte Carlo PENELOPE et des simulations XRT peut être utilisé pour prédire les réponses spectrales de l’instrumentation de fluorescence miniature pour différentes conditions géométriques dans le but de contribuer à l'améliorerX-ray fluorescence (XRF) is qualitative and quantitative analytical tool for elemental analysis of many types of materials; it is non-destructive, fast and is suitable for the analysis of the wide range of elements. The method is based on the excitation of an analyte by a beam of primary X-rays to induce the emission of X-ray fluorescence from the sample. The goal of the quantitative XRF analysis is to relate the elemental concentrations to the measured fluorescence intensities. However, this task is not straightforward since the apparent fluorescence intensities are dependent on the weight fraction of an analyte, matrix composition, geometry of the experimental setup, parameters of the primary X-ray source and detection system, etc.. The quantitative information can be obtained applying theoretical or empirical approaches. One of the aims of this thesis is to investigate the performances of the miniaturised XRF setup intended to the analysis of actinides by their L X-ray lines (12 keV < E < 17 keV) installed in the analysis laboratory within ATALANTE facility (CEA Marcoule). The experimental setup includes an Ag-anode X-ray tube which irradiates a sample, a silicon drift detector (SDD) and a cylindrical HOPG monochromator. The latter element is positioned between the sample and the detection system and in such a geometry, it acts as a bandpass filter modifying the spectral distribution of the fluorescence radiation. In this manner, the spectra can be recorded in the energy range of interest reducing the burden on the detection system from an unwanted radiation. The HOPG monochromator of the experimental setup cover the energy range of interest and permits to analyse analysis of medium-Z (Se, Rb, Sr, Y, etc.) and high-Z (mainly U, Np, Pu, Am, and Cm) elements by their K and L X-ray lines, respectively. The second goal of this work is to refine the classical quantification algorithm based on the fundamental parameters taking into account the modifications of the spectral distribution by the HOPG crystal. Indeed, spectra measured with a classical XRF system can be successfully processed using a theoretical method based on mathematical equations without standards. Such method is called the fundamental parameters (FP) method. However, in order to process accurately the spectra measured with the present setup, it arises the necessity to know the transmission function of the HOPG filter. The detailed investigation of the miniature setup and of the physical phenomena involved was performed utilizing the Monte Carlo method for the radiation transport with the PENELOPE code. In addition, to establish a better understanding of the reflection properties of the HOPG crystal, ray-tracing simulations were performed using the dedicated the ray-tracing package XRT to model the cylindrical HOPG crystal and represent step by step the entire detection channel. The response of the developed optical system was simulated applying the experimental spectra recorded without the HOPG monochromator as an input data. The validity of the simulation model has been approved through the comparison with experimental data for different liquid samples containing medium-Z elements (a few tens of mg.L-1),what allowed to define the HOPG transfer function. Next, the estimated transfer function could be successfully applied in the FP-based software PyMCA to provide quantitative results. To conclude, it is demonstrated that the coupling of the PENELOPE Monte Carlo code and XRT simulations can be used to predict the spectral responses of the miniature setup under different geometrical conditions in order to help to improve it
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Kalo, Kassem. "Caractérisation microstructurale et modélisation micromécanique de roches poreuses oolithiques." Thesis, Université de Lorraine, 2017. http://www.theses.fr/2017LORR0203/document.
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Le but de ce travail est d'étudier l'influence de la microstructure de roches poreuses hétérogènes sur le comportement à l'échelle macroscopique. Ainsi, nous avons caractérisé la microstructure et les propriétés micromécaniques (grâce à des tests de nano-indentation) de deux roches oolithiques poreuses (calcaire de Lavoux et minerai de fer) pour calculer leurs propriétés mécaniques et thermiques effectives. Les roches oolithiques sont constituées d'un assemblage de grains poreux (oolithes), de pores et de cristaux intergranulaires. La microscopie électronique à balayage et la tomographie 3D aux rayons X ont été utilisées pour identifier les différents composants de ces roches. Une attention particulière a été accordée à la tomographie aux rayons X car cette méthode analytique permet de caractériser le réseau poreux (taille, distribution spatiale et fraction volumique), ainsi que la forme des oolithes et des cristaux inter-oolithiques. La nouveauté de ce travail réside dans la prise en compte de la forme 3D réelle des pores. Par conséquent, nous avons approximé les oolites poreuses par des sphères et les pores de forme irrégulière par des ellipsoïdes. Cette approximation a été réalisée grâce à l'analyse en composantes principales (ACP), qui fournit les propriétés géométriques telles que la longueur des demi-axes et l'orientation des ellipsoïdes résultants. La sphéricité des oolites approximées a été calculée et les valeurs proches de 1 nous ont permis de considérer les oolithes comme des sphères. Pour vérifier l'approximation dans le cas des pores, nous avons évalué la contribution de ces pores tridimensionnels de forme irrégulière aux propriétés élastiques et thermiques effectives. Ainsi, les tenseurs de contribution de souplesse pour les pores irréguliers 3D et leurs approximations ellipsoïdales ont été calculés en utilisant la méthode des éléments finis (FEM). Ces tenseurs ont été comparés et une erreur relative a été estimée pour évaluer la précision de l'approximation. Cette erreur produit une distance maximale de 4,5% entre les deux solutions pour les pores et les ellipsoïdes, ce qui vérifie la procédure d'approximation proposée basée sur ACP. La méthode numérique FEM a été vérifiée en comparant la solution numérique des tenseurs de contribution des ellipsoïdes à la solution analytique basée sur la théorie d'Eshelby. La différence entre ces deux solutions ne dépasse pas 3%. La même méthode numérique a été utilisée pour calculer les tenseurs de contribution de résistivité thermique. Les tenseurs de souplesse et de résistivité calculés ont été utilisés pour évaluer les propriétés élastiques effectives (module élastique et coefficient de cisaillement) et la conductivité thermique effective en considérant le schéma d'homogénéisation de Maxwell en deux étapes. Les résultats ont montré une influence importante de la porosité sur les propriétés effectives. Enfin, les résultats obtenus pour les pores irréguliers ont été comparés à ceux des ellipsoïdes et ils ont montré un bon accord avec un écart maximal de 4% ce qui vérifie l'approximation des pores de forme irrégulière par des ellipsoïdes triaxiauxThe aim of this work is to study the influence of the microstructure of heterogeneous porous rocks on the behavior at the macroscopic scale. Thus, we characterized the microstructure and micromechanical properties (thanks to nano-indentation tests) of two porous oolitic rocks (Lavoux limestone and iron ore) to calculate their effective mechanical and thermal properties. Oolitic rocks are constituted by an assemblage of porous grains (oolites), pores and inter-granular crystals. Scanning electron microscopy and X-ray 3D Computed Tomography were used to identify the different components of these rocks. Particular attention was given to X-Ray computed tomography since this analytical method allows the characterization of the porous network (size, spatial distribution, and volume fraction), and the shapes of oolites and inter-oolitic crystals. The novelty of this work lies in taking into account the 3D real shape of pores. Hence, we approximated porous oolites by spheres and irregularly shaped pores by ellipsoids. This approximation was performed thanks to the principal component analysis (PCA), which provides the geometrical properties such as length of semi-axes and orientation of resulting ellipsoids. The sphericity of the approximated oolites was calculated and the values close to 1 allowed us to consider oolites as spheres. To verify the approximation in the case of pores, we evaluated the contribution of these irregularly shaped three-dimensional pores to the overall elastic properties. Thus, compliance contribution tensors for 3D irregular pores and their ellipsoidal approximations were calculated using the finite element method (FEM). These tensors were compared and a relative error was estimated to evaluate the accuracy of the approximation. This error produces a maximum discrepancy of 4.5% between the two solutions for pores and ellipsoids which verifies the proposed approximation procedure based on PCA. The FEM numerical method was verified by comparing the numerical solution for compliance contribution tensors of ellipsoids to the analytical solution based on Eshelby’s theory. The difference between these two solutions does not exceed 3%. The same numerical method was used to calculate thermal resistivity contribution tensors. Calculated compliance and resistivity contribution tensors were used to evaluate effective elastic properties (bulk modulus and shear coefficient) and effective thermal conductivity by considering the two-step Maxwell homogenization scheme. The results showed an important influence of the porosity on effective properties. Finally, the results obtained for irregular pores were compared to those for ellipsoidal ones and they showed a good agreement with a maximum deviation of 4% which verifies once again the approximation of irregularly shaped pores by tri-axial ellipsoids
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Khalili, Mohamed Hassan. "Tracking and modelling small motions at grain scale in granular materials under compression by X-Ray microtomography and discrete simulations." Thesis, Paris Est, 2016. http://www.theses.fr/2016PESC1128/document.
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Le travail réalisé durant cette thèse a été motivé par l'étude des mécanismes microscopiques à l'origine du fluage dans les matériaux granulaires.%En particulier, on cherche à explorer des techniques expérimentales et numériques pour l'étude d'un tel phénomène.Dans une première partie, on cherche à mesurer les déplacements des grains dans un matériau granulaire par observations en micro-tomographie X. Une telle identification ne peut être efficacement réalisée pour des phénomènes rapides avec les méthodes classiques de corrélation d'images numériques. Une nouvelle méthode nommée emph{corrélation discrète des projections numériques} qui contourne cette difficulté est développée dans cette thèse. Cette méthode, basée sur la corrélation des projections de tomographie, permet de mesurer les déplacements avec un nombre réduit de projections (100 fois moins que les méthodes classiques), ce qui diminue énormément le temps d'acquisition nécessaire pour la mesure. La méthode, appliquée à des données expérimentales, donne une précision comparable à celles des méthodes classiques tandis que le temps d'acquisition nécessaire est réduit à quelques minutes. Une étude portant sur l'analyse des sources d'erreurs affectant la précision des résultats est également présentée.Le but de la deuxième partie est de réaliser des simulations numériques pour fournir une caractérisation de l'essai oedométrique. Différents assemblages de billes de verre légèrement poly-disperses interagissant à travers des contacts élastiques de Hertz-Mindlin et frottement de Coulomb ont été utilisés. Ces simulations ont permis d'étudier l'évolution de certains paramètres structuraux du matériau modèle, préparant ainsi le terrain pour de futures études sur le fluage. Il a été particulièrement souligné que les contacts élastiques utilisés dans ces simulations ne reproduisent pas l'irréversibilité des déformations observée dans les expériences sur des sables. Cependant, l'irréversibilité est bien visible sur le nombre de coordination et l'anisotropie. Alors que les paramètres élastiques peuvent exprimer la réponse pour des petits incréments de déformations, la compression oedometrique est belle et bien anélastique, principalement à cause de la mobilisation du frottement. Le rapport entre les contraintes horizontales et verticales (coefficient du sol au repos) n'est particulièrement constant que lorsque l'anisotropie de structure est instaurée dans l'état initial de l'assemblage. Il est par ailleurs relié à l'anisotropie interne de la structure par une formule simple. Finalement, les coefficients du tenseur élastique dépendent principalement du nombre de coordination et son anisotropie est plus liée à l'anisotropie des contacts qu'à celle des forcesThe present work is motivated by the study of creep in granular materials at the microscopic scale.The first part of this thesis deals with displacement measurements by microtomography. Classical digital image correlation fails to catch time-dependent (possibly fast) phenomena such as short-term creep. A new method named emph{Discrete Digital Projection Correlation} is developed to overcome this limitation. This method requires very few projections (about 100 times less than classical methods) of the deformed state to perform the correlation and retrieve grain displacements. Therefore, the acquisition time is remarkably reduced, which allows to study time-dependent phenomena.The method is tested on experimental data. While its accuracy compares favorably to that of conventional methods, it only requires acquisition times of a few minutes. The origins of measurement errors are tracked by numerical means, on simulated grain displacements and rotations.The second part is a numerical simulation study, by the Discrete Element Method (DEM), of oedometric compression in model granular materials, carried out with a simple model material: assemblies of slightly polydisperse spherical beads interacting by Hertz-Mindlin contact elasticity and Coulomb friction. A wide variety of initial states are subject to compression, differing in density, coordination number and fabric anisotropy. Despite apparently almost reversible strains, oedometric compression proves an essentially anelastic and irreversible process,due to friction, with important internal state changes affecting coordination number and anisotropy. Elastic moduli only describe the response to very small stress increments about well equilibrated configurations. The ratio of horizontal stress to vertical stress (or coefficient of earth pressure at rest, commonly investigated in soil mechanics) only remains constant for initially anisotropic assemblies. A simple formula relates it to force and fabric anisotropy parameters, while elastic moduli are mainly sensitive to the latter. Further studies of contact network instabilities and rearrangements should pave the way to numerical investigations of creep behavior
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Noel, Claire. "Hydrodynamical simulations of detonations in superbursts." Doctoral thesis, Universite Libre de Bruxelles, 2007. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/210652.
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In this thesis, we construct a new hydrodynamical algorithm able of handling general compressible reactive flow problems, based on a finite-volume method inspired by the original MUSCL scheme of van Leer (1979). The algorithm is of second-order in the smooth part of the flow and avoids dimensional splitting. It uses MPI to achieve parallelism, and includes an astrophysical equation of state and a nuclear reaction network. It proves to be robust to tests cases. In particular it reproduces quite well the reactive and non-reactive results obtained with two different numerical methods (Fryxell & al. 1989, Busegnies & al. 2007). Moreover the time-dependent results are in agreement with the corresponding steady state solution. This gives us confidence in applying it to an astrophysical situation which has never been studied, the propagation of a detonation in conditions relevant to superbursts. The algorithm is described in (Noel & al. 2007).In a firt step we obtain the detonation profiles in pure carbon and in a mixture of carbon and iron. In both cases we underline the large difference between the total reaction length and the length on which some species burn. This difference leads to enormous numerical difficulties because all the length scales cannot be resolved at the same time in a single simulation. We show that the carbon detonation might be studied in a partial resolution approach like the one of Gamezo & al. (1999).
In a second step we construct a new reduced nuclear reaction network able to reproduce the energy production due to the photo-disintegrations of heavy elements, like ruthenium, which are thought to occur during superbursts in mixed H/He accreting systems. Using this new nuclear network we simulate detonations in mixture of carbon and ruthenium. An interesting feature is that, in this case, all the reaction lengths can be resolved in the same simulation. This makes the C/Ru detonations easier to study in future multi-dimensional simulations than the pure carbon ones (Noel & al. 2007b).
Finally we perform some numerical experiments which show that our algorithm is able to deal with initially inhomogeneous medium, and that the multi-dimensional simulations are attainable even if they are quite computational time consuming.
- B. Van Leer, J. Comp. Phys. 21, 101, 1979
- Fryxell, B.A. Muller, E. and Arnett, W.D. Technical report MPA 449, 1989
- Busegnies, Y. Francois, J. and Paulus, G. Shock Waves, 11, 2007
- Gamezo, V.N. Wheeler, J.C. Khokhlov, A.M. and Oran, E.S. ApJ, 512, 827, 1999
- Noël, C. Busegnies, Y. Papalexandris, M.V. & al. A&A, 470, 653, 2007
- Noël, C. Goriely, S. Busegnies, Y. & Papalexandris, M.V. submitted to A&A, 2007b
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Un algorithme parallèle basé sur une méthode aux volumes finis inspirée du schéma MUSCL de Van Leer (1979) a été construit. Il a été développé sur base de la méthode de Lappas & al. (1999) qui permet de résoudre simultanément toutes les dimensions spatiales. Cette méthode se base sur la construction de surfaces appropriées dans l'espace-temps, le long desquelles les équations de bilan se découplent en équations plus simples à intégrer. Cet algorithme est actuellement le seul à éviter le "splitting" des dimensions spatiales. Dans les modèles conventionnels (PPM, FCT, etc.), l'intégration spatiale des équations est réalisée de manière unidimensionnelle pour chaque direction.
Un réseau de réactions nucléaires ainsi qu'une équation d'état astrophysique ont été inclus dans l'algorithme et celui-ci a ensuite été soumis à une grande variété de cas tests réactifs et non réactifs. Il a été comparé à d'autres codes généralement utilisés en astrophysique (Fryxell & al. 1989, Fryxell & al. 2000, Busegnies & al. 2007) et il reproduit correctement leurs résultats. L'algorithme est décrit dans Noël & al. (2007).
Sur base de cet algorithme, les premières simulations de détonation dans des conditions thermodynamiques représentatives des Superbursts ont été réalisées. Différentes compositions du milieu ont été envisagées (carbone pur, mélange de carbone et de fer, mélange de carbone et de cendres du processus rp). Dans la plupart des systèmes où des Superbursts ont été observés, la matière accrétée est un mélange d'hydrogène et d'hélium. Dans ce cas, des phases de combustion précédant le Superburst produisent des nucléides plus lourd que le fer (Schatz & al. 2003). Ces nucléides peuvent être photodésintégrés durant le Superburst. Pour prendre en compte ces réactions endothermiques de photodésintégration, nous avons construit un nouveau réseau réduit de réactions nucléaires qui a été incorporé dans l'algorithme hydrodynamique (Noël & al. 2007b). Ce réseau réduit reproduit globalement l'énergétique d'un réseau complet et a permis de faire la première simulation numérique de détonation dans des conditions caractéristiques de systèmes accréteurs d'un mélange hydrogène-hélium.
Finallement quelques simulations multidimensionelles préliminaires ont éte réalisées.
- Busegnies, Y. Francois, J. and Paulus, G. Shock Waves, 11, 2007
- Fryxell, B.A. Muller, E. and Arnett, W.D. Technical report MPA 449, 1989
- Fryxell, B.A. Olson, K. Ricker, P. & al. ApJS, 131, 273, 2000
- Lappas, T. Leonard, A. and Dimotakis, P.E. SIAM J. Sci. Comput. 20, 1064, 1999
- Noël, C. Busegnies, Y. Papalexandris, M.V. & al. A&A, 470, 653, 2007
- Noël, C. Goriely, S. Busegnies, Y. & Papalexandris, M.V. submitted to A&A, 2007b
- Röpke, F. K. PhD thesis, Technischen Universitat Munchen, 2003
- Schatz, H. Bildsten, L. Cumming, A. and Ouellette, M. Nuclear Physics A, 718, 247, 2003
- Van Leer, B. Comp. Phys. 21, 101, 1979
- Weinberg, N.N. and Bildsten, L. ArXiv e-prints, 0706.3062, 2007
Doctorat en Sciences
info:eu-repo/semantics/nonPublished
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Finke, Justin David. "Monte Carlo/Fokker-Planck simulations of Accretion Phenomena and Optical Spectra of BL Lacertae Objects." Ohio University / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1181833339.
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Литвиненко, Д. О., and А. О. Ніколаєнко. "Інтерфейс програми для чисельного моделювання спектрів рентгенівської дифрації." Thesis, Сумський державний університет, 2014. http://essuir.sumdu.edu.ua/handle/123456789/38742.
Full textAbstract:
На сьогодні відомі різні чисельні методи, які дозволяють оцінити мікроструктуру плівкових матеріалів та її подальший вплив на фізичні властивості зразків. Більшість із таких методів обмежуються даними
досліджень, отриманими за допомогою растрової або просвічуючої електронної мікроскопії, атомно-силової мікроскопії, рентгенівського дифракційного аналізу. Проте, оскільки густина дефектів в плівках
дуже висока, то для їх виявлення в багатьох випадках роздільної здатності електронно-мікроскопічних зображень не достатньо. Тому замість традиційних підходів для вивчення мікроструктури плівок
(розміру кристалітів, дефектів кристалічної будови) активно застосовуються передові чисельні методи.
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Cavalcante, Fernanda Rocha. "Cálculo dos coeficientes de conversão de dose equivalente e dose efetiva em termos do kerma no ar para fótons utilizando simulador." Pós-Graduação em Física, 2013. https://ri.ufs.br/handle/riufs/5300.
Full textAbstract:
Dosimetric quantities are necessary for evaluate the human exposures to radiation quantitatively and to describe relationships between the dose and biological effects
caused by the interaction of radiation with the organs and tissues, providing a basis for
estimating risks in radiological protection. Anthropomorphic simulators are threedimensional
representations of the human body and coupled to a radiation transport
code provides conversion coefficients for estimating the equivalent and effective doses
through physical quantities, such as air kerma (Kair). In most published papers the
exposure scenarios consist of simulators implemented in the standing posture. In this
work we developed exposure scenarios in the Visual Monte Carlo (VMC) code using a
female adult voxel simulator in standing and sitting postures. The simulator was
irradiated by a plane source of monoenergetic photons with energy from 10 keV to
2 MeV in the antero-posterior (AP), postero-anterior (PA), right lateral (RLAT) and left
lateral (LLAT) irradiation geometries. The conversion coefficients for equivalent and
effective doses in terms of air kerma (H/Kair and E/Kair) were calculated for both
scenarios and compared. The results show that the relative difference of conversion
coefficients for the organs of the head and thorax was not significant (less than 5%) since
the anatomic position of the organs is the same in both postures. The relative difference
is more significant for organs of abdominal region, such as the ovaries (71% for photon
energy of 20 keV), the bladder (39% at 60 keV) and the uterus (37% at 100 keV),
especially when the simulator is irradiated in AP geometry. In this same irradiation
geometry, the conversion coefficients E/Kair presented relative differences until 27%
(at 10 keV), due to a change in absorbed dose of organs with relevant wT , which are
located in the anterior portion of the simulator. Thus, the calculation of conversion
coefficients HT / Kair and E/Kair using anthropomorphic simulators in different
postures is important for more precisely estimating of individual dose in real scenarios
of radiation exposure.Grandezas dosimétricas são necessárias para avaliar exposições dos seres humanos à radiação de modo quantitativo e para descrever relações entre a dose e os efeitos biológicos causados pela interação da radiação com os órgãos e tecidos, fornecendo uma base para estimativas de riscos em proteção radiológica. No âmbito computacional, os simuladores antropomórficos são representações tridimensionais do corpo humano que quando acoplados a um código de transporte de radiação fornecem coeficientes de conversão para estimativa de dose equivalente e dose efetiva através de grandezas físicas, como por exemplo, o kerma no ar (Kar). Na literatura, os cenários de exposição são, em geral, formados por simuladores implementados na postura vertical (em pé). Neste trabalho, foram elaborados cenários de exposição no código Visual Monte Carlo utilizando um simulador voxel adulto feminino nas posturas vertical e sentada. O simulador foi irradiado por uma fonte plana de fótons monoenergéticos de 10 keV a 2 MeV nas geometrias de irradiação antero-posterior (AP), postero-anterior (PA), lateral direita (RLAT) e lateral esquerda (LLAT). Os coeficientes de conversão de dose equivalente e dose efetiva em termos do kerma no ar (HT/Kar e E/Kar ) foram calculados para ambos cenários e comparados. Os resultados mostram que a diferença relativa entre os coeficientes de conversão HT /Kar?? para os órgãos da cabeça e do tórax não foi significante (menor que 6%) devido à posição anatômica dos órgãos ser a mesma para ambas posturas. Entretanto, a diferença relativa é significante para órgãos da região abdominal inferior, como ovários (71% para fótons de 20 keV), bexiga (39% em 60 keV) e útero (37% em 100 keV), principalmente quando o simulador é irradiado na geometria AP. Nesta mesma geometria, os coeficientes de conversão E/Kar apresentaram diferenças mais evidentes (27% em 10 keV), devido uma mudança na dose absorvida de órgãos com fatores de ponderação teciduais (wT ) relevantes, situados na porção anterior do simulador. Assim, o cálculo dos coeficientes de conversão HT /Kar e E/Kar utilizando simuladores antropomórficos em diferentes posturas é importante para estimar mais precisamente a dose em indivíduos submetidos a cenários reais de exposição à radiação.
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Maschio, Célio. "Desenvolvimento de metodos para avaliação de processos de filtração por meio de simulação por meio de simulação numerica e tomografia de raios-x." [s.n.], 2001. http://repositorio.unicamp.br/jspui/handle/REPOSIP/262896.
Full textAbstract:
Orientador: Antonio Celso Fonseca de ArrudaTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica
Made available in DSpace on 2018-07-31T14:51:24Z (GMT). No. of bitstreams: 1 Maschio_Celio_D.pdf: 13410400 bytes, checksum: bcad1a44963fabb3c498533b4663302a (MD5) Previous issue date: 2001
Resumo: O objetivo deste trabalho foi o desenvolvimento de metodologias para o estudo de filtros e processos de filtração, utilizando a tomografia de raios-X, técnicas de processamento digital de imagens e simulação numérica. Os ensaios convencionais utilizados pelos fabricantes são realizados através da medida de parâmetros, tais como pressão e vazão, em pontos localizados a montante e a jusante do filtro. Estes ensaios não são eficientes na caracterização de defeitos e não revelam como ocorre o processo de saturação no interior do filtro. Neste trabalho, a tomografia de raios-X foi utilizada para duas finalidades básicas: estudar a distribuição de contaminantes e analisar defeitos no interior de elementos filtrantes. Os modelos de filtração encontrados na literatura não levam em conta o efeito do acúmulo de contaminantes no desempenho do filtro ao longo do processo de filtração. Neste trabalho, foi desenvolvido um modelo acoplando-se as equações de filtração com as equações fenomenológicas (lei de Darcy e equação da continuidade), de tal forma que o acúmulo de partículas no meio poroso (filtro) fosse considerado na simulação do processo de filtração. Os resultados demonstraram que o processo de saturação no interior dos elementos analisados não ocorre de forma homogênea, ou seja, o acúmulo de partículas é predominante em determinadas regiões. Em geral, há formação de canais preferenciais e o espaço interno do filtro não é totalmente utilizado na captura de partículas. Demonstrou-se também que, em alguns casos, o comportamento do filtro não é coerente com a especificação do fabricante. Foi possível, por fim, a utilização dos dados experimentais, obtidos via tomografia, para a validação do modelo teórico desenvolvido
Abstract: The development of methods for analysis of filters and filtration process, using X-ray computerized tomography, digital image processing and numerical simulation, was the objective of this work. Tests conventionally used by filter manufacturers are made through the measurement ofparameters, such as flow and pressure, at upstream and downstream ofthe filter. These tests are not efficient in the characterization of defects and do not reveal how the saturation process occurs within the filter. In this work, X-ray computerized tomography was used for two basic purposes: to evaluate contaminant distribution and to detect defects within the interior of the filter elements. The filtration models found in the literature do not consider the effect of contaminant concentration on the filter efficiency during the filtration processo In this work, filtration equations and phenomenological equations (Darcy's law and continuity equation) were coupled and a model that takes into account the contaminant accumulation on the filter performance was developed. The results demonstrated that the saturation process within the analyzed filters is not homogeneous, that is, the accumulation of partic1es is predominant in some regions. Generally, there are preferential channels and the interior of the filter elements is not totally utilized. In some cases, it was also demonstrated that the filter behavior does not agree with the manufacturer specifications. Finally, it was possible to use the experimental data obtained with X-ray computerized tomography, in order to validate the theoretical developed model
Doutorado
Materiais e Processos de Fabricação
Doutor em Engenharia Mecânica
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Cozer, Thamara Cristina. "Análise de elementos traço presentes em tecidos mamários canino através da técnica de fluorescência de raios X." Universidade Tecnológica Federal do Paraná, 2016. http://repositorio.utfpr.edu.br/jspui/handle/1/1842.
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CAPESEstudos realizados com cães apontam que dos grupos tumorais analisados, os de mama representam cerca de 25% a 50% dos tipos de tumores. Deste total, metade é considerado maligno. Apesar de representar um valor considerável de malignidade, estudos nesta área são poucos representativos e escassos na literatura. É de conhecimento que os tumores são causados por mudanças químicas e bioquímicas que ocorrem na célula. Atualmente, pesquisas são realizadas para entender o comportamento dessas alterações e por este motivo é de grande valia conhecer os elementos traço presentes nestes tecidos. Para esta finalidade a técnica mais empregada é a de ED-XRF (Fluorescência de Raios X de Dispersão de Energia), uma vez que é uma técnica analítica não destrutiva que permite determinar e quantificar a composição elementar das amostras, porém não identifica elementos com baixos números atômicos (menor que Z=10). Foram analisadas 56 amostras de tecido mamário canino benignas e malignas, fixadas em formalina a 10% tamponada e mantida à temperatura ambiente. Primeiramente para a quantificação dos elementos traço Ca, Fe, Cu e Zn foram determinadas as curvas de calibração de padrões diluídos em água, com concentrações de Ca, Fe, Cu e Zn, variando de 400 mg/kg a 35 mg/kg, de 20 mg/kg a 2 mg/kg, de 10 mg/kg a 1 mg/kg e de 100 mg/kg a 9 mg/kg, respectivamente. As medições foram submetidas à técnica de ED-XRF utilizando um tubo de raios X com ânodo de prata e técnica de exposição de 30 kV e 100uA e um tempo de exposição de 1000 segundos (incerteza ≤ 3%). O código XRMC (X-Ray Monte Carlo) foi utilizado para validação do método experimental, que tem o objetivo de simular computacionalmente as respostas esperadas para os ensaios experimentais validando assim a eficácia da metodologia. As concentrações dos elementos traço obtidas foram analisadas estatisticamente onde verificou-se uma variação significativa do elemento Zn, estando este presente em maior concentração no tecido mamário maligno do que no benigno. Este resultado pode estar relacionado à presença deste elemento nas matrizes de metaloproteinases, e em neoplasias malignas estão mais concentradas porque há característica de invasão tumoral neste tipo de neoplasia. Em outra comparação estatística pode-se verificar que os elementos traços Fe, Cu e Zn tem concentração equivalente tanto na região central do tumor tanto quanto na periferia, com exceção do Ca, este concentrando-se mais na região tumoral o que pode se dever às calcificações. Estudos nessa área são de grande potencial por permitir um melhor entendimento do processo patológico em tumores mamários caninos.
Studies with dogs show that the breast cancer represent about 25% to 50% of tumor types. Of this total, half is considered malignant. Despite representing a considerable amount of malignancy, studies in this area are few representative and scarce in the literature. It is known that tumors are caused by chemical and biochemical changes that occur in the cell. Currently, surveys are conducted to understand the behavior of these changes and for this reason, it is of great value to know the trace elements present in these tissues. For this purpose, the most common technique is to ED-XRF (X-Ray Fluorescence Energy Dispersion) since it is a non-destructive analytical technique to determine and quantify the elemental composition of the samples, although it doesn’t identify elements with low atomic numbers (less than Z= 10). Were analyzed 56 samples of canine breast tissue benign and malignant, fixed in 10% buffered formalin and kept at ambient temperature. First, for the measurement of trace elements Ca, Fe, Cu and Zn were determined standards for calibration curves diluted in water to concentrations of Ca, Fe, Cu and Zn, ranging from 400 mg/kg to 35 mg/kg, from 20 mg/kg to 2 mg/kg, from 10 mg/kg to 1 mg/kg and from 100 mg/kg to 9 mg/kg, respectively. Measurements were subjected to ED-XRF technique using an X-ray tube with silver anode and exposure technique of 30 kV and 100 uA and exposure time of 1000 seconds (uncertainty ≤ 3%). The XRMC code (X-Ray Monte Carlo) was used for validation of experimental method, which is intended to simulate by computer the expected responses for experimental tests, therefore validating the methodology efficiency. The concentrations of trace elements obtained were analyzed statistically where there was a significant variation of Zn element, the latter being present in higher concentration in malignant breast tissue than benign. This result may be related to the presence of this element in the matrix metalloproteinases, and malignant neoplasms are more concentrated because there are characteristic of tumor invasion in this type of neoplasm. In another statistical comparison it can be seen that the trace elements Fe, Cu and Zn is equivalent concentration both in the central region of the tumor as well as in the periphery, with the exception of Ca, this focusing more on the tumor region may be due to calcifications. Studies in this area are of great potential for allowing a better understanding of the disease process in canine mammary tumors.
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Cedola, Alessia. "Production de faisceaux de rayons-X submicroniques par guide d'onde en couches minces." Université Joseph Fourier (Grenoble ; 1971-2015), 1999. http://www.theses.fr/1999GRE10040.
Full textAbstract:
Dans cette these on decrit une nouvelle technique utilisant un guide d'onde pour rayons x pour produire un faisceau de dimension submicronique et on presente les proprietes du faisceau autant que un certain nombre d'applications possibles. Le premier chapitre est dedie a une presentation des techniques traditionnelles de production de faisceaux submicroniques. Dans le chapitre ii on presente de facon generale le sujet des ondes stationnaires et la resonance qui se forment dans une couche de materiel leger depose entre deux couches de materiel plus lourd. La resonance produit un faisceau submicronique dont on a mesure les caracteristiques : dimensions geometriques, divergence et coherence. Les performances de la guide d'onde sont aussi discutees avec un regard particulier pour le flux, l'efficience et le gain du systeme et pour les elements qui deteriorent les performances memes. On conclut le chapitre avec une comparaison entre les performances de la guide d'onde et d'autres systemes optiques. Dans le troisieme chapitre on traite la technique du contraste de phase pour l'imagerie a haute resolution. Apres une introduction generale sur cette technique, on presente des mesures de formation d'images par contraste de phase obtenues avec le faisceau submicronique sortant d'une guide d'onde pour rayons x. En ce cas un role tres important est joue par l'agrandissement de l'image due a la divergence angulaire du faisceau, qui permet de se passer de la resolution du detecteur. La comparaison des resultats des mesures faites sur un test pattern avec des simulations numeriques montre qu'une resolution de 0. 1 micron peut etre obtenue. On montre aussi que les donnees experimentales de l'image defocalise peuvent etre elaborees numeriquement pour reconstruire une image reelle de l'objet comparable a celle obtenue avec le microscope electronique.
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Iglesias, Susana Marrero. "Simulação e análise de gradientes de tensão em materiais e ligas metálicas." Universidade do Estado do Rio de Janeiro, 2008. http://www.bdtd.uerj.br/tde_busca/arquivo.php?codArquivo=788.
Full textAbstract:
As tensões residuais influenciam o comportamento mecânico dos metais e ligas. O campo de tensões pode determinar o desempenho do material. Então, torna-se de grande
importância o estudo e a determinação das tensões residuais. O método padrão da difração de raios X para medir tensões s residuais (Método sen2ψ ) apresenta limitações na determinação de tensões caracterizadas por alto gradiente. È por isso que o estudo do gradiente de tensão superficial é um dos mais importantes problemas teóricos e experimentais em mecânica, especialmente no caso da análise de tensões superficiais que surgem após vários tipos de tratamentos superficiais, como: processamento por laser e tecnologia de implantação iônica. A simulação computacional e os métodos
numéricos nos dão a possibilidade de resolver os problemas da determinação dos parâmetros do gradiente de tensão. Neste trabalho foi desenvolvida e aplicada a modelação e simulação computacional para o estudo do comportamento de materiais na
presença de distribuições de tensão caracterizadas por alto gradiente. Foi aplicada a modelagem para diferentes tipos de tensões com gradiente para metais puros e ligas metálicas. Foi determinada uma forma para usar a modelagem no caso de materiais compósitos e são apresentados resultados para o caso do silumínio, mostrando o comportamento similar deste material compósito aos materiais puros como aço e
alumínio. Usando a análise de Fourier, foi determinada a função de distorção nos casos de perfis alargados pela existência de gradiente de tensão. Foi determinada também a relação entre as funções de atenuação e de tensão na função de distorção e são apresentados resultados para diferentes tipos de distribuições de tensão. Ademais, foi desenvolvida uma metodologia para a determinação dos parâmetros do gradiente de tensão usando a simulação computacional das linhas de difração desenvolvida neste trabalho. A metodologia desenvolvida é baseada na simulação dos perfis de difração distorcidos pelo gradiente de tensão superficial e na análise destas distorções. Das metodologias desenvolvidas para a determinação de distribuições de tensões para o caso de gradiente, a que usa transformada de Fourier é matematicamente correta, porem apresenta dificuldades na determinação das funções de gradiente para casos de
distribuições muito complexas e na determinação dos relacionamentos das escalas das funções envolvidas no processo de deconvolução. A alta complexidade deste método e
os problemas numéricos que acarreta nos levam a propor a metodologia desenvolvida usando as larguras integrais dos perfis de difração para a determinação aproximada da função de distribuição de tensões. Esta metodologia é de simples aplicação e a sua precisão dependerá da quantidade de dados determinados na simulação direta para a obtenção dos gráficos de calibração.The residual stress influences the mechanical behavior of metals and alloys. The stress field can determine the material performance. Then, become of great importance the study and determination of residual stress field. The standard X-ray diffraction method for residual stress measurement ent ( sen2ψ Method) presents limitations in the strong stress gradient determination. For that reason, the superficial stress gradient determination is one of the most important theoretical and experimental problem in engineering, especially in the analysis of the stress gradients due to surfaces treatments as laser or ionic implantation. The computational simulation and numerical methods give us the possibility of solve this problems. In this work is developed and applied two methods of modeling and simulation for the study of the material behavior with strong stress gradient. Is applied this modeling technique for different stress distribution in pure metals and metallic alloys. Is established a methodology for the composite material cases and is presents the results for the case of siluminium, showing that the behavior is similar to the other metals testing as steel and aluminum. Also, using Fourier analysis is determined the distortion function for the broadened profiles in the presence of stress gradient. In this work is shown the relation between the attenuation and stress distribution functions in the distortion. Is shown, results for several stress distribution functions. Moreover, is developed a methodology for the determination of stress gradient parameters using the computational simulation of the diffraction lines also developed in this work. The methodology is based in the simulation of the profiles broadened by stress gradient and the analysis of these distortions. Of the developed methodologies for the determination of stress distribution functions for the gradient case, the one that uses Fourier analysis is mathematically correct, but presents difficulties in the determination of the gradient functions for cases of complex stress distributions and in the scales determination of the functions involved in the deconvolution process. The high complexity of this method and the numeric problems that it carries leaves as, to propose the use of the developed methodology using the integral breath of the diffraction profiles for the approximate determination of the stress distribution function. The methodology application is simple and its accuracy will depend on the amount of data determined in the direct simulation to obtain the calibration graphics.
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Zeiske, Tim. "Understanding complex biomolecular systems through the synergy of molecular dynamics simulations, NMR spectroscopy and X-Ray crystallography." Thesis, 2016. https://doi.org/10.7916/D8TX3F60.
Full textAbstract:
Proteins and DNA are essential to life as we know it and understanding their function is understanding their structure and dynamics. The importance of the latter is being appreciated more in recent years and has led to the development of novel interdisciplinary techniques and approaches to studying protein function. Three techniques to study protein structure and dynamics have been used and combined in different ways in the context of this thesis and have led to a better understanding of the three systems described herein.
X-ray crystallography is the oldest and still arguably most popular technique to study macromolecular structures. Nuclear magnetic resonance (NMR) spectroscopy is a not much younger technique that is a powerful tool not only to probe molecular structure but also dynamics. The last technique described herein are molecular dynamics (MD) simulations, which are only just growing out of their infancy. MD simulations are computer simulations of macromolecules based on structures solved by X-ray crystallography or NMR spectroscopy, that can give mechanistic insight into dynamic processes of macromolecules whose amplitudes can be estimated by the former two techniques.
MD simulations of the model protein GB3 (B3 immunoglobulin-binding domain of streptococcal protein G) were conducted to identify origins of discrepancies between order parameters derived from different sets of MD simulations and NMR relaxation experiments.The results highlight the importance of time scales as well as sampling when comparing MD simulations to NMR experiments. Discrepancies are seen for unstructured regions like loops and termini and often correspond to nanosecond time scale transitions between conformational substates that are either over- or undersampled in simulation. Sampling biases can be somewhat remedied by running longer (microsecond time scale) simulations. However, some discrepancies persist over even very long trajectories. We show that these discrepancies can be due to the choice of the starting structure and more specifically even differences in protonation procedures. A test for convergence on the nanosecond time scale is shown to be able to correct for many of the observed discrepancies.
Next, MD simulations were used to predict in vitro thermostability of members of the bacterial Ribonuclease HI (RNase H) family of endonucleases. Thermodynamic stability is a central requirement for protein function and a goal of protein engineering is improvement of stability, particularly for applications in biotechnology. The temperature dependence of the generalized order parameter, S, for four RNase H homologs, from psychrotrophic, mesophilic and thermophilic organisms, is highly correlated with experimentally determined melting temperatures and with calculated free energies of folding at the midpoint temperature of the simulations. This study provides an approach for in silico mutational screens to improve thermostability of biologically and industrially relevant enzymes.
Lastly, we used a combination of X-ray crystallography, NMR spectroscopy and MD simulations to study specificity of the interaction between Drosophila Hox proteins and their DNA target sites. Hox proteins are transcription factors specifying segment identity during embryogenesis of bilaterian animals. The DNA binding homeodomains have been shown to confer specificity to the different Hox paralogs, while being very similar in sequence and structure. Our results underline earlier findings about the importance of the N-terminal arm and linker region of Hox homeodomains, the cofactor Exd, as well as DNA shape, for specificity. A comparison of predicted DNA shapes based on sequence alone with the shapes observed for different DNA target sequences in four crystal structures when in complex with the Drosophila Hox protein AbdB and the cofactor Exd, shows that a combined ”induced fit”/”conformational selection” mechanism is the most likely mechanism by which Hox homeodomains recognize DNA shape and achieve specificity.
The minor groove widths for all sequences is close to identical for all ternary complexes found in the different crystal structures, whereas predicted shapes vary between the different DNA sequences. The sequences that have shown higher affinity to AbdB in vitro have a predicted DNA shape that matches the observed DNA shape in the ternary complexes more closely than the sequences that show low in vitro affinity to AbdB. This strongly suggests that the AbdB-Exd complex selects DNA sequences with a higher propensity to adopt the final shape in their unbound form, leading to higher affinity.
An additional AbdB monomer binding site with a strongly preformed binding competent shape is observed for one of the oligomers in the reverse complement strand of one of the canonical (weak) Hox-Exd complex binding site. The shape preference seems strong enough for AbdB monomer binding to compete with AbdB-Exd dimer binding to that same oligomer, suggested by the presence of both binding modes in the same crystal. The monomer binding site is essentially able to compete with the dimer binding site, even though binding with the cofactor is not possible, because its shape is very close to the ideal shape.
A comparison of different crystal structures solved herein and in the literature as well as a set of molecular dynamics simulations was performed and led to insights about the importance of residues in the Hox N-terminal arm for the preference of certain Hox paralogs to certain DNA shapes. Taken together all these insights contribute to our understanding of Hox specificity in particular as well as protein-DNA interactions in general.
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Bootsma, Gregory James. "Physics and Computational Methods for X-ray Scatter Estimation and Correction in Cone-beam Computed Tomography." Thesis, 2013. http://hdl.handle.net/1807/65456.
Full textAbstract:
X-ray scatter in cone-beam computed tomography (CBCT) is known to reduce image quality by introducing image artifacts, reducing contrast, and limiting computed tomography (CT) number accuracy. The extent of the effect of x-ray scatter on CBCT image quality is determined by the shape and magnitude of the scatter distribution in the projections. A method to allay the effects of scatter is imperative to enable application of CBCT to solve a wider domain of clinical problems. The work contained herein proposes such a method.
A characterization of the scatter distribution through the use of a validated Monte Carlo (MC) model is carried out. The effects of imaging parameters and compensators on the scatter distribution are investigated. The spectral frequency components of the scatter distribution in CBCT projection sets are analyzed using Fourier analysis and found to reside predominately in the low frequency domain. The exact frequency extents of the scatter distribution are explored for different imaging configurations and patient geometries.
Based on the Fourier analysis it is hypothesized the scatter distribution can be represented by a finite sum of sine and cosine functions. The fitting of MC scatter distribution estimates enables the reduction of the MC computation time by diminishing the number of photon tracks required by over three orders of magnitude.
The fitting method is incorporated into a novel scatter correction method using an algorithm that simultaneously combines multiple MC scatter simulations. Running concurrent MC simulations while simultaneously fitting the results allows for the physical accuracy and flexibility of MC methods to be maintained while enhancing the overall efficiency. CBCT projection set scatter estimates, using the algorithm, are computed on the order of 1-2 minutes instead of hours or days. Resulting scatter corrected reconstructions show a reduction in artifacts and improvement in tissue contrast and voxel value accuracy.
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"Automatic extraction of bronchus and centerline determination from CT images for three dimensional virtual bronchoscopy." 2000. http://library.cuhk.edu.hk/record=b5890498.
Full textAbstract:
Law Tsui Ying.Thesis (M.Phil.)--Chinese University of Hong Kong, 2000.
Includes bibliographical references (leaves 64-70).
Abstracts in English and Chinese.
Acknowledgments --- p.ii
Chapter 1 --- Introduction --- p.1
Chapter 1.1 --- Structure of Bronchus --- p.3
Chapter 1.2 --- Existing Systems --- p.4
Chapter 1.2.1 --- Virtual Endoscope System (VES) --- p.4
Chapter 1.2.2 --- Virtual Reality Surgical Simulator --- p.4
Chapter 1.2.3 --- Automated Virtual Colonoscopy (AVC) --- p.5
Chapter 1.2.4 --- QUICKSEE --- p.5
Chapter 1.3 --- Organization of Thesis --- p.6
Chapter 2 --- Three Dimensional Visualization in Medicine --- p.7
Chapter 2.1 --- Acquisition --- p.8
Chapter 2.1.1 --- Computed Tomography --- p.8
Chapter 2.2 --- Resampling --- p.9
Chapter 2.3 --- Segmentation and Classification --- p.9
Chapter 2.3.1 --- Segmentation by Thresholding --- p.10
Chapter 2.3.2 --- Segmentation by Texture Analysis --- p.10
Chapter 2.3.3 --- Segmentation by Region Growing --- p.10
Chapter 2.3.4 --- Segmentation by Edge Detection --- p.11
Chapter 2.4 --- Rendering --- p.12
Chapter 2.5 --- Display --- p.13
Chapter 2.6 --- Hazards of Visualization --- p.13
Chapter 2.6.1 --- Adding Visual Richness and Obscuring Important Detail --- p.14
Chapter 2.6.2 --- Enhancing Details Incorrectly --- p.14
Chapter 2.6.3 --- The Picture is not the Patient --- p.14
Chapter 2.6.4 --- Pictures-'R'-Us --- p.14
Chapter 3 --- Overview of Advanced Segmentation Methodologies --- p.15
Chapter 3.1 --- Mathematical Morphology --- p.15
Chapter 3.2 --- Recursive Region Search --- p.16
Chapter 3.3 --- Active Region Models --- p.17
Chapter 4 --- Overview of Centerline Methodologies --- p.18
Chapter 4.1 --- Thinning Approach --- p.18
Chapter 4.2 --- Volume Growing Approach --- p.21
Chapter 4.3 --- Combination of Mathematical Morphology and Region Growing Schemes --- p.22
Chapter 4.4 --- Simultaneous Borders Identification Approach --- p.23
Chapter 4.5 --- Tracking Approach --- p.24
Chapter 4.6 --- Distance Transform Approach --- p.25
Chapter 5 --- Automated Extraction of Bronchus Area --- p.27
Chapter 5.1 --- Basic Idea --- p.27
Chapter 5.2 --- Outline of the Automated Extraction Algorithm --- p.28
Chapter 5.2.1 --- Selection of a Start Point --- p.28
Chapter 5.2.2 --- Three Dimensional Region Growing Method --- p.29
Chapter 5.2.3 --- Optimization of the Threshold Value --- p.29
Chapter 5.3 --- Retrieval of Start Point Algorithm Using Genetic Algorithm --- p.29
Chapter 5.3.1 --- Introduction to Genetic Algorithm --- p.30
Chapter 5.3.2 --- Problem Modeling --- p.31
Chapter 5.3.3 --- Algorithm for Determining a Start Point --- p.33
Chapter 5.3.4 --- Genetic Operators --- p.33
Chapter 5.4 --- Three Dimensional Painting Algorithm --- p.34
Chapter 5.4.1 --- Outline of the Three Dimensional Painting Algorithm --- p.34
Chapter 5.5 --- Optimization of the Threshold Value --- p.36
Chapter 6 --- Automatic Centerline Determination Algorithm --- p.38
Chapter 6.1 --- Distance Transformations --- p.38
Chapter 6.2 --- End Points Retrieval --- p.41
Chapter 6.3 --- Graph Based Centerline Algorithm --- p.44
Chapter 7 --- Experiments and Discussion --- p.48
Chapter 7.1 --- Experiment of Automated Determination of Bronchus Algorithm --- p.48
Chapter 7.2 --- Experiment of Automatic Centerline Determination Algorithm --- p.54
Chapter 8 --- Conclusion --- p.62
Bibliography --- p.63